This invention relates to a container vessel or cassette and an erasure device for a stimulable phosphor sheet. More particularly, it relates to a cassette provided with the function of erasing residual radiation images on the stimulable phosphor sheet and especially that of secondary erasure of erasing useless energies stored in the sheet until the sheet is used for image recording. It also relates to an erasure device for a stimulable phosphor sheet capable of erasing the sheet while contained in the cassette, that is, without the necessity of taking the sheet out of the cassette.
One of typical prior art methods for obtaining radiation images as picture images is a radiation system using a radiation film having an emulsion layer comprising a silver halide photo-sensitive material in combination with a sensitizing paper. As a substitute for the radiation system, attention is recently drawn to a radiation image recording and reproducing system using a stimulable phosphor.
Certain phosphors, when exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, electron beams and ultraviolet rays, store part of the energy the radiation possesses. When the phosphor is subsequently exposed to a stimulating ray such as visible light, it produces stimulated emission corresponding to the stored energy. The phosphor exhibiting such properties is known as a stimulable phosphor.
There is proposed a system for recording and reproducing radiation image information using the stimulable phosphor. In such a system, the radiation image information of an object such as a human body is first stored in a sheet having a layer of stimulable phosphor (referred to as "stimulable phosphor sheet" or simply "phosphor sheet", hereinafter). The sheet is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The emitted light is detected by a photoelectric detector to obtain image signals as electrical signals. The image signals are processed to provide a radiation image of the object ready for diagnosis. Reference is made to U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, and 4,387,428 and Japanese Patent Application Kokai No. 56-11395.
The radiation image information recording/reproducing system includes an image reading unit for reading a radiation image stored in a stimulable phosphor sheet. The following is illustrative of the procedure for the reading unit to read the radiation image.
The stimulable phosphor sheet with the radiation image stored and recorded therein is enclosed in the cassette. The cassette with the phosphor sheet contained therein are loaded into the image reading device. The cassette is then opened and the sheet is taken out of the cassette by leafing means. The sheet is then conveyed as by a conveyor to a reading unit. In the reading unit, the sheet is conveyed in one direction by mechanical means to effect sub-scanning, while the sheet is irradiated with a light beam, such as the laser beam, which is deflected in a direction substantially orthogonal to the sheet conveying direction, to effect main scanning. The light thus produced by stimulated emission is sensed chronologically by a photo sensor such as a photomultiplier to produce an image information. The produced image information is ultimately reproduced as a hard copy or reproduced on a display system such as CRT. The stimulable phosphor sheets from which the image information has been read-out are transported to an erasure device where they are irradiated with an erasure light beam emanating from the light source, such as fluorescent-, tungsten-, halogen-, xenon- or sodium lamp, for erasing residual radiation images, after which they are stacked in a stacker tray.
It will be noted that, after termination of reading and subsequent erasure for releasing the residual radiation energies at the erasure device or section, referred to hereafter as the primary erasure, the stimulable phosphor sheet contained in the stacker tray is exposed to radiation rays such as those emitted from radioactive isotopes contained in minor amounts in the phosphor or intruded into the tray or natural radiations such as electro-magnetic-, cosmic- or diffused X-rays, so that unnecessary energies are stored in the sheet. When the sheet is subsequently employed for recording the image information, these noises are presented as the noise to affect the image information adversely. For this reason, the sheet is subjected again to erasure, referred to hereafter as the secondary erasure, before it is used for signal recording.
Conventionally, the secondary erasure is carried out by any of the following methods.
(i) The stimulable phosphor sheet is transported by a transport device to an erasure unit for primary erasure on the same line as that used for reading. After termination of the secondary erasure at the erasure unit, the sheet is returned into the stacker tray which is then accommodated in the cassette. Reading is not carried out at this time in the erasure unit.
(ii) The stimulable phosphor sheet is taken out of the stacker tray before it is used for signal recording. The sheet is subjected to secondary erasure by a separate erasure unit provided outside of the image reading unit.
(iii) The stimulable phosphor sheet it subjected to secondary erasure unit for secondary erasure which is provided in the vicinity of a loader adapted for introducing the stimulable phosphor sheet from the stacker tray into the cassette.
In the above method (i), the sheet need to be circulated once again on the same line as that used for reading, before it is re-used for signal recording, thus resulting in loss of time. In addition, the device is used exclusively during this time for secondary erasure so that it cannot be used for reading other sheets, thus resulting in the lowered operational efficiency. The cassette needs to be loaded into the device for each secondary erasure with increased labor expenses.
The phosphor sheet is circulated for secondary erasure once on the same transport line as that used for reading, thus resulting in loss of time. In addition, there is the increased likelihood that the surface of the stimulable phosphor sheet is scored during transport to detract from the image quality.
In the methods (ii) and (iii), a separate erasure unit needs to be provided outside of the image reading device or in the vicinity of the loader. In the method (ii), increased time and labor are involved in carrying out the secondary erasure.
In the method (iii), since the secondary erasure is carried out while the stimulable phosphor sheet is introduced for storage into the cassette, secondary erasure needs to be carried out subsequently in cases wherein the sheet is not used directly after it is stored in the cassette but used only after lapse of a prolonged time.
In addition, in the above methods (ii) and (iii), since it is necessary that the stimulable phosphor sheet be taken out of the cassette and returned into the cassette by manual operation after it is subjected to the secondary erasure by the separate erasure device, the sheet is directly touched by hand, so that fingerprints or hand dirts may be adhered to the sheet surface.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to obviate the above deficiencies of the prior art and to provide a cassette for a stimulable phosphor sheet endowed with the function of erasure according to which the time and labor involved in the erasure and above all in the secondary erasure of the sheet may be obviated without the necessity of providing the separate unit dedicated to secondary erasure, and the erasure operation can be positively carried out without relevance to the storage time in the cassette.
It is another object of the present invention to provide an erasure device for a stimulable phosphor sheet according to which the time and labor involved in the erasure and above all in the secondary erasure of the sheet may be eliminated and the erasure operation may be carried out positively without damage or attachment of dirts to the sheet surface.
For accomplishing the above objects, the present inventors conducted eager research, and arrived at the concept of endowing the cassette accommodating the stimulable phosphor sheet with the function of erasure such that the erasure may be carried out directly before photographing.
On the basis of the above finding, the first aspect of the present invention resides in a cassette for a stimulable phosphor sheet comprising a casing accommodating a stimulable phosphor sheet therein and a cover pivotally mounted to the casing for opening and closure, wherein light reflecting means are provided therein for reflecting or diffusing the light introduced from outside the cassette for irradiation on an image recording region of the stimulable phosphor sheet.
In the above first aspect of the present invention, the light reflecting means preferably comprises a light reflecting surface on the inner surface of the cover for reflecting or diffusing the light.
According to the second aspect of the present invention, there is provided a cassette for a stimulable phosphor sheet comprising a casing accommodating the stimulable phosphor sheet and a cover mounted to said casing for opening and closure, wherein light transmitting means are provided therein for transmitting the light introduced from outside the cassette for irradiation on an image recording region of the stimulable phosphor sheet.
In the above second aspect, the light transmitting means are preferably provided therein the register with the image recording region of the stimulable phosphor sheet accommodated in the cassette, the light transmitting means comprising a light transmitting member having an inlet for external light, with light barrier means being provided for intercepting the light otherwise introduced into the inlet for external light.
According to the third aspect of the present invention, there is provided a cassette for a stimulable phosphor sheet comprising a casing accommodating the stimulable phosphor sheet and a cover mounted to the casing for opening and closing, wherein a light source and light transmitting means are provided therein, the light transmitting means transmitting the light from the light source for irradiation on the image recording region on the stimulable phosphor sheet.
In the above third aspect, the light transmitting means include a light transmitting member provided in register with the image recording region of the stimulable phospor sheet and having an inlet for light emitted by the light source.
According to the fourth aspect of the present invention, there is provided a cassette for a stimulable phosphor sheet comprising a casing for the stimulable phosphor sheet and a cover mounted to the casing for opening and closing, wherein light emitting means are provided at least in register with the image recording region of the stimulable phosphor sheet accommodated therein.
In the above fourth aspect, the light emitting means are preferably provided on the inner side of the casing.
In the above fourth aspect, the light emitting means are preferably provided on the inner side of the cover.
In the above fourth aspect, the light emitting means are preferably light emitting diodes.
According to the fifth aspect of the present invention, a device for erasing radiation energies stored in a stimulable phosphor sheet by irradiating an erasure light on the sheet, comprising a housing, means provided in the housing for opening a cassette placed at a predetermined position within said housing, the cassette accommodating the stimulable phosphor sheet to be erased, and a light source device provided in the housing for irradiating the erasure light on the stimulable phosphor sheet within the cassette which is in the opened state.
In the above fifth aspect, cassette transport means are preferably provided for transporting the cassette to the predetermined position in the housing from outside the housing and also out of the housing from the predetermined position.
In the above fifth aspect, only one cassette can be contained in the housing, the one cassette being transported into the device and then transported therefrom after erasure.
In the above fifth aspect, a plurality of cassettes can be contained in the housing and adapted to be erased separately or simultaneously.
The image recording area herein designates the overall surface of the stimulable phosphor sheet when the effective image information is recorded on the sheet surface in its entirety, and a portion of the sheet surface when the effective image information is recorded on such portion, as when the object is placed at the center of the sheet for recording.